Generally, a microphone is a device that converts a sound into an electrical signal. A microphone may be used in various communication apparatuses such as mobile communication apparatuses, earphones, hearing aids, and the like.
Microphones have been required to have good sound performance, reliability, and operability.
In addition, microphones have been recently gradually miniaturized. Therefore, a microelectromechanical systems (MEMS) microphone using a MEMS technology has been developed.
The MEMS microphone has stronger moisture resistance and heat resistance than those of an electret condenser microphone (ECM) according to the related art, and may be miniaturized and integrated with a signal processing circuit.
MEMS microphones are divided into omni-directional microphones and directional microphones depending on the directional characteristics thereof. An omni-directional microphone is a microphone having uniform sensitivity in all directions with respect to an incident sound wave. A directional microphone is a microphone having different sensitivities depending on a direction of an incident sound wave, and is divided into a unidirectional microphone, a bidirectional microphone, and the like, depending on directional characteristics thereof. For example, the directional microphone is used in a recording operation performed in a narrow room or when only a desired sound is received in a room having large reverberation.
Since vehicles are in an environment where a sound source may be distant and noise is variably generated, a microphone robust to changes in a noise environment is required, and a unidirectional microphone that can receive a sound source only in a desired direction may be used in order to implement a microphone robust to changes in the noise environment.
When a MEMS microphone is packaged, a hole through which a sound may pass in a substrate is formed. Substrates include a printed circuit board (PCB), a ceramic substrate, or the like. Then, a die is attached and fixed onto the substrate by an epoxy or the like.
Therefore, according to the related art, in the MEMS microphone, in the case in which the size of a sound inlet formed in the substrate and the size of the sound hole of the microphone are different from each other, undesired resonance is generated, and an example of this resonance may include Helmholtz resonance generated between a narrow sound hole and a large sound inlet formed in the substrate.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.